Polyolefins such as high density polyethylene (HDPE) homopolymer and linear low density polyethylene (LLDPE) copolymer can be produced using various combinations of catalyst systems and polymerization processes. Chromium based and Ziegler based catalyst systems can, for example, produce polymer resins having good processibility, typically due to their broad molecular weight distribution (MWD). In contrast, polymers produced using catalyst systems containing a single metallocene compound generally have a narrow MWD and, accordingly, poor processibility. Broad MWD and bimodal resins can be made from dual metallocene catalyst systems.
However, some broad MWD bimodal resins can experience processing issues, such as melt fracture, due to the disparity in molecular weights of the two components of the MWD. Moreover, chromium based and Ziegler based catalyst systems often produce polymers in which more of the comonomer is present in the lower molecular weight fraction of the polymer. The presence of more comonomer in the higher molecular weight fraction of the polymer, often referred to as a reverse comonomer distribution or a reverse short chain branching distribution (SCBD), often can improve physical properties in various end-use applications.
In view of these generalities, it would be beneficial to produce broad molecular weight distribution polymers having a reverse comonomer or reverse SCBD. Accordingly, it is to these ends that the present invention is directed.